Experts are warning that the common habit of leaving leftover chicken or pizza on the table overnight out of laziness could lead to food poisoning.
Primrose Freestone, a professor of clinical microbiology at the University of Leicester in the United Kingdom, outlined safe storage methods for leftover food in a contribution to academic media outlet The Conversation on Tuesday. According to Freestone, dried herbs sprinkled on pizza — such as basil, pepper and oregano — can harbor food poisoning bacteria including Salmonella and Bacillus cereus. Even if the heat from a freshly baked pizza kills the bacteria, leaving it at room temperature for an extended period allows the remaining toppings to become a breeding ground for germs. Freestone stressed that pizza should be covered and refrigerated within two hours of delivery or preparation and consumed within two days. This is because refrigeration only slows bacterial growth but does not completely prevent it.
Leftover chicken requires even greater caution. Chicken meat is rich in moisture and nutrients and has low acidity, making it an ideal environment for bacterial growth. Freestone warned that if any trace of pink or blood is visible in cooked chicken, it signals undercooked portions and should be discarded immediately. Since it is difficult to determine contamination by smell or color alone, chicken that will not be eaten right after cooking should be covered and refrigerated within two hours and consumed within three days.
Rice dishes are trickier than pizza or chicken. Spores of Bacillus cereus found in uncooked rice are heat-resistant and can survive the cooking process. When left at room temperature for more than two hours, the spores can germinate back into bacteria and produce toxins. Freestone explained that severe vomiting and diarrhea can persist for up to 24 hours. Fried rice or risotto should be cooled quickly after cooking, refrigerated and consumed within 24 hours.
Leftover canned food should be covered and refrigerated, though transferring it to an airtight container is preferable for taste. Freestone advised that high-acid foods such as tomatoes can be kept refrigerated for five to seven days, but low-acid items including meat, fish and vegetables should not be stored for more than three days.